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Review of The vestibular system

Review of The vestibular system . Two classes of sensory subsystems: 3 crista: encode angular acceleration Located in the ampulla at the terminus of each of 3 fluid-filled semi circular canals The inertial force of the fluid provides the basis for moving hair bundles.

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Review of The vestibular system

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  1. Review of The vestibular system • Two classes of sensory subsystems: • 3 crista: encode angular acceleration • Located in the ampulla at the terminus of each of 3 fluid-filled semi circular canals • The inertial force of the fluid provides the basis for moving hair bundles • Otolith organs: encode linear acceleration • Two types: • Utricle (Horizontal acceleration) • Saccule (vertical acceleration) • Located in the utricle • The inertial force of the otoliths provides the basis for moving hair bundles

  2. In both subsystems the hair cell is used to transduce head movement information • At rest there is a continuous intermediate level of NT release • Hair cells depolarize or hyperpolarize depending direction of cilium movement • Towards kinocilium depolarized (increases NT release) • Away from kinocilium hyperpolarizes (decreases NT release) • Note that all output from the vestibular organs exit the boney labyrinth via the VIII cranial nerve (vestibular-cochlear nerve) An interesting link: http://www.bio.davidson.edu/people/midorcas/animalphysiology/websites/2005/Cowell/index.htm

  3. The vestibular system pathways: Overview • Vestibular system output travels the VII CN splits and terminates in the brain stem: • Cerebellum (movement coordination) • Vestibular nuclei. Four nuclei: • Superior • Lateral • Medial • Inferior • Output from the vestibular nuclei project • Up ipsilaterally and contralaterally to optic motor control areas (compensatory eye movements) • Down the spinal chord in two pathways to control motor output (balance and posture control)

  4. The vestibular system pathways Location of primary and secondary brainstem nuclei • Vestibular nuclei • Project to cerebellum, PPRF and spine • Paramedian pontine reticular formation • projects to abducens • Abducens • Project to lateral rectus muscle and contralateral oculomotor nucleus • Trochlear nucleus • superior oblique muscle of the eye • Oculomotor nucleus • Several extra ocular muscles

  5. Vestibular nuclei

  6. Vestibulospinal projections: The lateral vestibular nucleus/spinal tract • Descends the ipsilateral spinal chord • Terminates at all levels of the spine. • Excitatory pathway activates postural muscles (proximal to spine) to correct for leftward listing.

  7. Vestibulospinal projections: The medial vestibular nucleus/spinal tract • Descends ipsilateral and contralateral spinal chord but asymmetrically • Terminates in the cervical and thoracic spine. • Excitatory pathway activates postural muscles (proximal to spine) mainly in the neck.

  8. Ascending projections to oculomotor nuclei • Both direct contralateral and indirect ipsilateral control of extra ocular muscles • Counters head movements to keep image stable on retina. • Damage of vestibular nerve/nuclei causes nystagmus a oscillation of horizontal eye movement.

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